feat(deploy): automatic hardlink repair built into deployment pipeline

User insight: hardlink breakage only happens at deploy time (scp file
replacement / git checkout-merge), so detection must be welded INTO the
deploy pipeline, not left to daily audit.

Three automatic layers, no reliance on discipline:
1. systemd path watcher (profile-scripts-sync.path): watches
   deploy/profile-scripts/ directory, auto-fires sync_profile_scripts.sh
   on any change. Verified: fires within 4s of file replacement, logs to
   gateway/logs/link_sync.log (runs as hmo user)
2. git hooks (.git/hooks/post-merge + post-checkout on 246 repo):
   auto re-link after git operations
3. Manual fallback: sync_profile_scripts.sh (now self-logging)

dev-spec red line #6 updated: SSOT rule now documents the three layers
and states breakage only happens at deploy time.

scripts/git-hook-post-merge.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+# git post-merge / post-checkout hook — 自动重建硬链接
+# git 操作（merge/checkout/rebase）会替换文件、破坏硬链接，钩子自动修复
+REPO="/home/hmo/MoFin"
+if [ -x "$REPO/deploy/profile-scripts/sync_profile_scripts.sh" ]; then
+    bash "$REPO/deploy/profile-scripts/sync_profile_scripts.sh" >/dev/null 2>&1
+    echo "$(date '+%F %T') auto-synced by git $1 hook" >> "$REPO/gateway/logs/link_sync.log"
+fi
+exit 0